Some conventional electrical current sensors are positioned near a current-carrying conductor to sense a magnetic field generated by the current through the conductor. The current sensor generates an output signal having a magnitude proportional to the magnetic field induced by the current through the conductor.
Current sensors can be arranged in either an open loop or a closed loop configuration. An “open loop” current sensor includes a magnetic field transducer in proximity to a current-carrying, or primary, conductor. The magnetic field transducer provides an output signal proportional to the magnetic field generated by current passing through the primary conductor. A “closed loop” current sensor additionally includes a secondary conductor in proximity to the magnetic field transducer. A current is passed through the secondary conductor in order to generate a magnetic field that opposes and cancels the magnetic field generated by a current passing through the primary conductor. In some closed loop current sensors, a measure of the secondary conductor current can provide an indication of the level of the current passing through the primary conductor.
Some current sensors can include more than one magnetic field sensing element spaced from each other and positioned at different distances from the primary conductor. In such systems, a difference between the magnetic field, as sensed by each of the spaced elements, can be indicative of the current passing through the primary conductor.
The accuracy with which a magnetic field-based current sensor senses an intended current can be affected by its immunity to stray magnetic fields. Some conventional current sensors employ shields, sometimes in the form of a ferrite or other magnetic core positioned around the conductor, to concentrate the magnetic field in the vicinity of the sensor and to thereby provide a level of shielding against stray fields, such as those that may be caused by currents flowing in adjacent conductors.